"Many schools are vulnerable to violent intruders entering the building with a weapon and causing harm to the occupants. A secondary threat to the school is the introduction of a portable explosive device into the building to cause mass casualties," the report said.

The report recommended that schools maintain a security force, install closed-circuit TVs, upgrade locks, hold regular drills and take other safety measures aimed at reducing the threat. It also provided guidance for lockdown and evacuation procedures.

"There may never be perfection, as no security measure is perfect; however, risks can be significantly reduced," the report said.

The report said the presence of security forces varies widely across the state and depends on factors like cost and public perception.

"An unarmed security officer is less effective in dealing with a more serious security incident, such as a violent intruder," it noted.

Donald Smith, emergency planning and response coordinator for the nonprofit Center for Safe Schools in Camp Hill, said most schools are already following some of the recommendations. He said the number of security staff in schools has increased "exponentially" since last year's Sandy Hook Elementary School massacre and more are looking into using armed personnel.

The state Legislature passed a quadrupled $8.5 million school safety bill in response to the mass shooting in Newtown, Conn., while in northeastern Pennsylvania, many schools have beefed up security over the past year, according to the Pocono Record.

At Delaware Valley School District, for example, Superintendent John Bell said officials made $500,000 in security improvements in response to Newtown.